Biology Reference
In-Depth Information
7.2.2
Changes linked to adaptation to depth and changes of pressure
7.2.2.1
Skin
During the sedentary growth phase, the back of the eel is greenish brown
and the ventral face is creamy white with yellow bands, while at the time
of the oceanic migration of reproduction, they are respectively blackish
brown and silvery white (Fig. 2). The silvering of the skin is thought to
be the result of the increase of dorsal melanin and ventral purines (Bertin,
1951; Pankhurst and Lythgoe, 1982). In addition to this change in color, the
skin becomes thicker (Bertin, 1951; Pankhurst, 1982a). Other skin changes
also occur resulting in a greater resistance to abrasion, as increase in
mucus production (Bertin, 1951; Saglio et al., 1988) and variation in scales
(Pankhurst, 1982a).
Figure 2
. European eel yellow and silver stages. Note the silvery color of the ventral side
of the silver eel as compared to the yellow eel. The eye diameter is enlarged in silver eels
compared to yellow eels.
Color image of this figure appears in the color plate section at the end of the topic.
7.2.2.2
Eye
Eye is probably one of the most modifi ed sensory organs during eel silvering.
Indeed, during the sedentary phase, eel is a benthic fi sh and lives in rivers,
where conditions for vision can be poor. In contrast, in the open ocean,
conditions for vision are better even considering that in depth only few light
goes through (Lythgoe, 1979). In deep sea, photosensitive pigments have
maxima absorption displaced towards the blue end of the spectrum (Denton
